The Pt $L_3$ edge and the Ni K edge extended x-ray-absorption fine-structure (EXAFS) measurements have been made on amorphous (${\mathrm{Ni}}_{\mathrm{x}}$${\mathrm{Pt}}_{100\mathrm{-}\mathrm{x}}$${)}_{75}$${\mathrm{P}}_{25}$ alloys at three low temperatures as well as at room temperature. With a limited k range, the Fourier transforms of the Pt $L_3$ and the Ni K EXAFS for amorphous Ni-Pt-P alloys exhibit extremely broad peaks which manifest an unusually large disorder of the system. As the maximum k range of the transformation is extended with an enhanced signal-to-noise ratio, these broad major peaks in the Fourier transforms still remain broad and begin to split into two and finally into three. The relative magnitudes and the thermal variation of these three split peaks strongly indicate the existence of subshells for different atomic pairs such as Pt-P, Pt-Ni, and Pt-Pt. Though it is not possible, at present, to determine the degree of asymmetry in the radial distribution of each subshell, a rough simulation of the split peaks in the Fourier transforms of the Pt $L_3$ EXAFS data at 7 K for two compositions of amorphous Ni-Pt-P provides further evidence for the existence of separate subshells for different atomic pairs. Moreover, while the thermal disorder is apparently greater for a Pt-Pt pair subshell than those of the two other subshells, the structural disorder seems to be greater for a Pt-Ni pair subshell than that for a Pt-Pt subshell.

• Received 27 January 1987

DOI:https://doi.org/10.1103/PhysRevB.36.4613